Concentration of dilute acetic acid



i Patented Apr. 1l2", 1927.

UNITED Q STATES HERMANN suina, or ironLING, AUSTRIA.

-. CONCENTRATION OF DILUTE ACETIC ACID.

application niefa June 1s, 1924, serial No. 7zo,s12, lana m Austria :une 26, 192s.

The copending patent application Serial NNO. 720,811, filedA of even date herewith relates' to a process for thejmaiiufacture of concentrated acetic acid from diluted acetic acid, according to .which process acetic acid can be extracted from its diluted aqueous solutions by means of solvents whichare insoluble or soluble with diiiculty in water, dissolve acetic acid and have a considerably higher boiling point than that of the pure acetic acid. The acetic acid thus extracted `may be separated from the solvent in a more concentrated state, by suitable distillation. According to that process of extraction, as

in all other hitherto known processes of ex `aqueous solution, butfit differs from the other processes in that a portion of the extraction means isintroducedin the .form of vapours, which shows that theprocess of said patent only uses extracting substances which have a lower boiling point than that of thev aqueous acetic 'acid submitted to extraction.

It has been found that the efiiciency of the method of working describedfin my cepending application Serial No. 720,811, filed 'of even date herewith can be considerably improved by causing the diluted, aqueous acetic acid under treatment to pass in the form of vapours in the opposite direction to thcex-l tracting substance which is still liquid i at that temperature. The unexpected result of this modified method of working is that the extraction of acetic acid from its aqueous mixture is much more complete than when the extraction is carried outwith both substances in the form of a liquid, under otherwise identical conditions and with the'same height of the extraction column. l

The accompanying ldrawing shows diagraiirimatically by way of example an appa` ratus for carrying out the process.

The diluted aqueous acetic acid-is heated to boiling ina boiler 1 which is continuousl fed with fresh diluted acetic, acid throng -a pipe 2, andthe escapingvapours 'of'w'ater and aceticr acid pass through a pipe 3 into the bottom of a laterally arranged distilling column 4 of any `desired construction, which is filled say with clay balls 9. vOn rising in the column 4, lthevapours meet with a shower of the extracting substance of` a higher .boiling point admit-ted through a sprayer 5 at the top of the column and preferably preheated in a lieatiexclianger 6. The water vapours, almost completely deprived of acetic. acid, escape at the top of thecolumn 4 through apip'e 7 and are either condensed in an adjoining heat exchanger 6, or utilized elsewhere for secondary heating purposes. The extracting substance, which has absorbed the acetic acid from the vapours and is charged with acetic acid, passes while still hot at the bottom of the column 4 under theppe 3 through Siphon 8, and is used directly for conversion into concentrated acetic acid and solvent. For this purpose the solution is subjected to a Afractional distillation in which the acetic acid is distilled 'off whereas the solvent remains practically free from aceticacid as a residue and is returned for re-use in the extraction process. The reason Why the acetic acid passes in liquid state into the extracting substance Vin spite of the temperature inthe column,

is that vthe Vapour tension of acetic acid in liquids which have a high dissolving capacity and a higher boiling point than acetic acid, is considerably reduced, while the Water vapour tension does not experience any m'aterial reduction, since the water vapours are practically insoluble inthe solvents used accordin'g to the invention. The` solvents for carrying out the present processare chiefly suitable organic liquids containing oxygen, for instance7 `organic substances containing the yhydroxyl group, with a boiling 'point above 150 C. Among them may he meiitioned, monovalent phenols, except carbolic acid, such as c'resols and polyvalent phenols more particularlyA in thel form of their- 5 ethers, suoli as for instance guajacol, its homologues and4 similar phenols, hydrated phenols, for instance l1exa-hydro-cresol's,'eli

phatic and cyclic ketons with high boiling point, further fatty acids with high boiling .the vapors of tliedilute acid with a liquid solvent which has a boiling point above 150 point,`and'finally natural or artificial mix- I C., said solvent having a high 'capacity for' g Y g 1,624,811

dissolving acetic acid but a low capacit for C., said solvent havin 'ya high capacit/yh'for 10 dissolving water, then treating the so vent dissolvingacetic acidgutavlow capacit' for containing the acetic acid toseparate the dissolving wateri'atheiidis'tiliing the so ,vent4 acetic acid and returning the solvent-for recontainind the actic acid to separate the 5 use in the process. acetic aci and returning the solvent for rel 2. A process for the concentration' of'diuse in the process.. lute acetic acid, which comprises extracting l In testimonywhereof I have hereunto set the vapors of the dilute acid with a liquid my hand. solvent which basa boiling point above 150? v HERMANN SUIDA. 

